1. Field of the Invention
This invention relates to an electric motor assembly, more particularly to an electric motor assembly that has a braking arrangement to stop immediately rotation of the motor once power to drive the motor is switched off.
2. Description of the Related Art
The improvement of this invention is directed to a conventional electric motor with a braking arrangement, which is disclosed in U.S. Pat. No. 4,460,838 and which is illustrated in FIGS. 1 and 2. As illustrated, the conventional electric motor includes a rotor shaft 10, an armature assembly 11, a stop plate 12, a spring 13, a rotating clutch plate 14, and a pawl member 15. The rotating clutch plate 14 is rotatable with the rotor shaft 10. Normally, the armature assembly 11 is located at the position shown in FIG. 1. When power to drive the motor is switched on, a magnetic field is created to move the armature assembly 11 to the position shown in FIG. 2, in which a pawl portion 151 of the pawl member 15 is moved out of the rotational path of a lobe portion 141 of the rotating clutch plate 14. When the power to drive the motor is switched off, the spring 13 biases the armature assembly 11 back to the position shown in FIG. 1, in which the pawl portion 151 of the pawl member 15 extends through an aperture 120 in the stop plate 12 into the rotational path of the lobe portion 141 of the rotating clutch plate 14, thereby stopping rotation of the clutch plate 14 and the rotor shaft 10. The conventional electrical motor suffers from the following disadvantages:
(1) The engagement of the lobe portion 141 with the pawl portion 151 causes serious damage to engaging surfaces between the pawl member 15 and the rotating clutch plate 14 due to the rapid movement of the pawl member 15 from the position of FIG. 2 to that of FIG. 1. As a result, the pawl member 15 and the rotating clutch plate 14 might be struck to deform or even break.
(2) When the power to drive the motor is switched off, the rotor shaft 10 does not stop immediately, thereby resulting in inconvenience in use, e.g. for exerciser applications.